This invention relates to values for modulating fluid flow in refrigeration systems. While the invention is described in particular detail with respect to such systems, those skilled in the art will recognize the wider applicability of the valve disclosed hereinafter.
Diaphragm valves incorporting pilot valve actuation are well known in the art. In general, these values include a flexible diaphragm interposed between the valve input and the valve output sides. The diaphragm has a bleed opening in it, and higher pressure fluid from the valve input side is allowed to equalize the forces acting on first and second sides of the diaphragm. When the main valve is to be activated, a pilot valve is opened which quickly relieves pressure on the first side of the diaphragm, permitting the high pressure fluid on the second side of the diaphragm to lift the diaphragm, thereby opening the main fluid passageway through the valve.
It has been common to employ a solenoid to actuate the pilot portion of the valve in prior art diaphragm valve constructions. The solenoid generally is operatively connected to the pilot valve so that energization of the solenoid opens the pilot valve while de-energization of the solenoid closes the pilot valve. The pressure differential on opposite sides of the diaphragm caused by pressure relieved through the pilot valve is used to lift the diaphragm. While prior art diaphragm valves have functioned satisfactorily, in the past such valves have been characterized by single point operation. That is to say, the valves operate at one of two positions, fully on or off, and diaphragm valves have not been capable of modulating the flow through the main fluid passageway. In addition, in applications where the main inlet fluid pressure fluctuates over relatively wide range, solenoid operated valves have been known to operate unsatisfactorily. Thus, at high input pressures, the rating of solenoid may be insufficient to permit operation and failure of the solenoid results. While pilot operation of the diaphragm valve was intended to avoid solenoid burn out, at low input pressures, the differentials on each side of the diaphragm may be insufficient to open the diaphragm and flow through the valve becomes unpredictable.
A number of solutions have been proposed to overcome the problems associated with solenoid actuation of the diaphragm valve. For example, the United States Patent to Schnittker, U.S. Pat. No. 3,943,947, assigned to the assignee of the present invention, is specifically designed to overcome problems associated with diaphragm actuation at low input pressures.
While the prior art in general, and Schnittker in particular, works for its intended purpose, the diaphragm actuated valve disclosed hereinafter offers superior performance capability while eliminating many deficiencies encountered with prior art diaphragm actuated valves. Surprisingly, we have found that diaphragm valves can be utilized to modulate fluid flow through a valve by controlling flow through the pilot valve so that the forces acting on the diaphragm attain equilibrium relationship at a variety of diaphragm positions. This is accomplished by utilizing a heat motor axially arranged with respect to a valve stem mounted for movement in the pilot valve opening of the diaphragm. The valve stem is directly driven by the heat motor to precise relative position with respect to the pilot valve opening.
There are special considerations encountered in employing a modulating heat motor with a piloted diaphragm valve. We have found that the simple combination of heat motor and valve often results in unstable operation. That is to say, the diaphragm will oscillate rapidly rather than maintain an equilibrium position in response to pilot pin position. The unstability is particularly prevalent at high pressure differentials which often occur in refrigeration systems. We have found that heat motors can be successfully employed in modulating diaphragm valve if the valve incorporates structure for reducing the instability. Such structure, in the embodiment illustrated, includes a specially designed flow baffle positioned below the diaphragm, and a friction damper in the form of guide fingers which are movable with the valve stem.
One of the objects of this invention is to provide a diaphragm actuated valve capable of modulating fluid flow through the valve.
Another object of this invention is to provide a low cost modulating valve construction.
Another object of this invention is to provide a pilot controlled diaphragm actuated valve in which the pilot valve has a positive force acting to close it.
Another object of this invention is to provide a valve construction which permits valve actuation regardless of the pressure differential between the outlet and the inlet side of the valve.
Another object of this invention is to provide a modulating valve construction which provides improved stability over the operating range of the valve.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.